1. Field of the Invention
The present invention relates to supporting construction of lower links and check chains for anti-roll of the lower links of a working machine attaching linkage, especially, a three-point hitch linkage which is vertically movably provided on a front or rear portion of a working vehicle.
2. Related Art
As is well-known, an agricultural tractor of conventional utility is provided at the rear portion thereof with a working machine attaching linkage for attaching a working machine like a rotary cultivator, a tedder or a mower. A three-point hitch linkage comprising a top link, left and right lower links, left and right lift arms, left and right lift rods and left and right check chains is typical. The top link is pivotally supported by a link hitch fixedly provided on the rear surface of a transmission casing of the vehicle. The lower links are pivotally supported by respective brackets which are fixed to left and right rear axle casings provided on both sides of a rear portion of the transmission casing or are fixed to the transmission casing. The lower ends of the lift rods are pivoted on intermediate portions of the lower links, respectively and the upper ends thereof are pivoted on rear ends of the lift arms, respectively. The lift arms extend from a hydraulic lifting device on the transmission casing. The check chains are interposed between intermediate portions of the lower links and the rear axle casings or the brackets, respectively.
With regard to such a working machine attaching linkage, Japanese Utility Model Laid-Open Gazette No. Sho 63-112403 describes that a front end of each lower link is pivoted on a pivotal member provided on each side surface of a transmission casing. A front end of each check chain is pivoted on another pivotal member provided on each rear axle casing, coaxially with the pivotal member on the transmission casing.
Japanese Utility Model No. Sho 57-56641 and Japanese Utility Model Laid-Open Gazette No. Sho 59-92604 describe that a pivotal shaft is supported by a supporting member projecting rearwardly from each side of the transmission casing or from each rear axle casing so as to project both laterally and outwardly from the supporting member. The front end of each lower link and the front end of each check chain are pivoted on one and the other side portions of the pivotal shaft, respectively, about the supporting member.
Deviation of the front ends of the lower link and the check chain from each other with respect to their pivotal axes during vertical rotation of the linkage causes modification or abrasion of the pivotal members or others. In the two types of conventional constructions, the former type has the advantage of preventing the front ends of the lower link and the check chain from such deviation because the pivotal members provided on the transmission casing and the rear axle casing, respectively, are coaxial with each other. However, coaxially and respectively disposing the pivotal members on the transmission casing and the rear axle casing is difficult and expensive because it is necessary to ensure accuracy of the parts.
The second type also has the advantage of preventing the front ends of the lower link and the check chain from such deviation because both of the front ends thereof are pivoted on the same pivotal shaft. However, as the distance between the lower link and the check chain decreases, there is a reduction in the anti-rolling effect of the check chain. If the distance is increased, deformation of the pivotal shaft occurs because it is supported at its intermediate portion by only one supporting member. If the pivotal shaft is thickened for reinforcement, it is necessary to expand the supporting member proportionally.